The amino acid GABA (γ-aminobutyric acid) is the main inhibitory neurotransmitter in the adult mammalian brain and regulates many physiological and psychological processes. GABA acts through two major classes of receptors: ionotropic GABAA (including GABAC) receptors and metabotropic GABAB receptors (Hill and Bowery, Nature 1981, 290, 149-152; Bormann, J., Trends Pharmacol. Sci. 2000, 21, 16-19). GABAB receptors are present in most regions of the mammalian brain on presynaptic terminals and postsynaptic neurons, and are involved in the fine-tuning of inhibitory synaptic transmission. Due to their strategic position in neuronal networks to modulate the activity of the various neurotransmitter systems, GABAB receptors are a target of choice for pharmacological agents intended to treat central and peripheral nervous systems disorders (Bettler et al., Physiol Rev. 2004, 84, 835-867; Cryan and Kaupmann, Trends Pharmacol Sci. 2005, 26, 36-43).
The GABAB receptor belongs to the Class-III family of G protein-coupled receptors (GPCRs), as are the receptors for glutamate, Ca2+, pheromones and putative taste compounds (Pin et al., Pharmaco. Ther. 2003, 98, 325-354). All members of this family share the characteristic of a large extracellular amino-terminal domain that contains a so-called “Venus Flytrap” orthosteric ligand binding site and seven transmembrane (7TM) helical segments plus an intracellular carboxyl-terminal domain that are involved in receptor activation and G-protein coupling (Bockaert and Pin, EMBO J. 1999, 18, 1723; Galvez et al, J. Biol. Chem. 1999, 274, 13362-13369). A distinct feature, however, of the GABAB receptor is that it operates as a heterodimer of at least two homologous subunits termed GABAB1 and GABAB2 (Kaupman et al, Nature 1997, 386, 239-246; Gordon et al, J. Biol. Chem. 1999, 12, 7607-7610; Margeta-Mitrovic et al, PNAS 2001, 98, 14649-14654; Bettler et al, Physiol Rev. 2004, 84, 835-867). Orthosteric GABAB receptor ligands bind only at the N-terminal Venus flytrap region of the GABAB1 subunit, which in turn activates the associated GABAB2 subunit of the heterodimer. It is this later subunit that is responsible for coupling and activation of G-protein (Galvez et al, EMBO J. 2001, 20, 2152-2159; Duthey et al, J. Biol. Chem. 2002, 277, 3236-3241; Pin et al, Biochem. Pharmacol. 2004, 68, 1565-1572). The resulting effect is an inhibition of the adenylyl cyclase activity and subsequent cyclic AMP formation and the modulation of activity of inwardly rectifying potassium channels and voltage-sensitive calcium channels.
Several studies using knock-out (KO) mice have demonstrated the role of the heterodimeric GABAB1B2 receptor in several CNS disorders. Mice lacking the GABAB1 subunit exhibit spontaneous seizures and hyperalgesia (Schuler et al, Neuron 2001, 31, 47-58). These behavioral characteristics are paralleled by a loss of all biochemical and electrophysiological GABAB responses in these KO mice. In these studies, a clear impairment of passive avoidance performance was also observed indicating impaired memory processes. GABAB1 deficient mice were also found to be more anxious than their wild-type counterparts (Mombereau et al, Neuropsychopharmacology 2004, 29, 1050-1062). Analogous results were obtained with GABAB2 KO mice, which presented all the same behavioural characteristics than the one observed for the GABAB1 KO mice (Gassman et al, J. Neurosci. 2004, 24, 6086-6097). Moreover, it has also been shown that a hypoactivity of the GABA system was linked to spasticity, epilepsy, anxiety, stress, sleep disorders, depression, addiction, and pain (Dalvi and Rodgers, Psychopharmacology 1996, 128, 380-397; for a recent review Ong and Kerr, CNS Drug Dev. 2005, 11, 317-334); while on the contrary, a hyperactivity of the GABAergic system was associated with schizophrenia (Blum and Mann, Int. J. Neuropsychopharmacol. 2002, 5, 159-179).
Baclofen is a potent and selective agonist at the GABAB receptor and is presently a frequently and only used clinical drug in the treatment of spasticity and rigidity (Montane et al, Neurology 2004, 63, 1357-1363). Moreover, all effective pharmacological agents used to treat panic disorder increase GABA synaptic transmission and anxiolytics and antidepressants that lack GABA activity are not effective in panic disorders. Baclofen was shown to be significantly effective in reducing the number of panic attacks and symptoms of anxiety as assessed with the Hamilton anxiety scale, Zung Scale, and Katz-R nervousness subscale (Breslow et al, Am. J. Psychiatry 1989, 146, 353-356). Drake and co-workers, hypothesized that baclofen would be an effective treatment in the symptomatic management of veterans with chronic posttraumatic stress disorder (PTSD). Their results demonstrated that the therapy, well tolerated, resulted in significant improvements of the overall symptoms of PTSD and co-morbid depression and anxiety in patients with chronic PTSD due to combat (Drake et al, Ann. Pharmacother. 2003, 37, 1177-1181). More recently, a study looking at the effect of baclofen on the prepulse inhibition (PPI) of the acoustic startle response (ASR), proposed GABAB receptors as putative new targets in the pharmacological therapy of psychotic disorders (Bortalo et al, Psychopharmacology 2004, 171, 322-330). Despite the demonstration of baclofen as being a potential therapeutic tool for the treatment of disorders such as anxiety and spasticity, its use has been limited due to its poor blood-brain-barrier penetration, very short duration of action, muscle relaxing property, hypothermic and sedative side effects, as well as patients' increasing tolerance (Hefferan et al, Neuroscience Letters 2006, 403, 195-200).
A new avenue for developing selective compounds acting at GPCRs is to identify molecules that act through allosteric mechanisms, modulating the receptor by binding to a site different from the highly conserved orthosteric binding site. This concept has assumed a greater importance in the pharmacology of family III receptors in general. For example, allosteric modulators have been described for Ca2+-sensing receptors (Nemeth et al, U.S. Pat. No. 6,031,003), for metabotropic glutamate receptors (reviewed in Mutel, Expert Opin. Ther. Patents 12:1-8, 2002; Ritzen, Mathiesen and Thomsen, Basic Clin. Pharmacol. Toxicol 97:202-13, 2005), and most recently for GABAB receptors (Urwyler et al, Mol. Pharmacol. 2001, 60, 963-971; WO 2005/094828; WO 2006/001750; WO 2006/063732; WO 2006/048146; WO 2006/07486; WO 2006/136442; WO 2007/014843; US 2007/027204; WO 2007/073297; WO 2007/073298; WO 2007/073299; WO 2007/073300). These ligands do not activate the receptor by themselves, but, for example in the case of the GABAB receptor, increase the potency of GABA in the presence of this endogenous agonist (Pin et al, Mol. Pharmacol. 2001, 60, 881-884; Urwyler et al, Neuropharmacol. 2005, 48, 343-353). Mutational analyses have demonstrated unequivocally that the binding of known GABAB receptor positive allosteric modulators does not occur at the orthosteric site, but instead at an allosteric site within the seven transmembrane region of the GABAB2 subunit at least for CGP7930 (Binet et al, J. Biol. Chem. 2004, 279, 29085-29901).
As a therapeutic principle, positive allosteric modulators are expected to have several advantages over compounds acting as orthosteric agonists, because they are only effective in the presence of the endogenous ligand and therefore act in line with physiological neurotransmission in its temporal and spatial organization. Orthosteric agonists, on the other hand, activate receptors independently of synaptic activity, possibly leading to unwanted side effects.
Cryan and co-workers suggested in a recent study, using GS39783 (N,N′-Dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine), that a positive modulation of GABAB receptors may serve as a novel therapeutic strategy for the development of anxiolytics with a better side effect profile as compared to baclofen (Cryan et al, J. Pharm. Exp. Therap. 2004, 310, 952-963). They showed that GS39783 is active in models of anxiety such as elevated plus maze (rat), elevated zero maze (mice and rats), and the stress-induced hyperthermia (mice) tests. Moreover, as expected for a positive allosteric modulator that do not have any effect on receptor activity in absence of GABA, but do enhance allosterically the affinity of the GABAB receptor for the endogenous GABA, no side effect on locomotor activity, rotarod, body temperature and traction test was observed for doses ranging from 0.1 to 200 mg/kg, p.o. In comparison baclofen presented those side effects even at efficacious doses in anxiety models. In conclusion, those data suggest that GS39783, and positive allosteric modulators of GABAB receptors in general, are useful and innovative anxiolytics without side-effects associated with baclofen. An interesting example of the use of such compounds in preclinical studies have been done for CGP7930 and GS39783 for the treatment of Gastro-Esophageal Reflux Disease (GERD) and cocain self-administration in rats, where those compounds were found active (Smith et al, Psychopharmacology 2004, 173, 105-111; WO 03/090731).
Recently the 3,3′-diarylpropyl-1-arylethylamines and 3-aryl propyl-1-arylethylamine have been reported as a new class of GABAB receptor modulators as they potentiate baclofen-induced responses in the brain (Kerr et al, Aust. J. Chem. 2006, 59, 445-456) and they modulate both pre- and postsynaptic GABAB receptors in rat brain slices (Ong et al, Eur. J. Pharm. 2005, 507, 35-42).
Patent Publications DE10255416 and WO9730980 describe triazinediones derivatives having herbicidal properties. These triazinediones are also described in the field of fungicide (EP0438717), growth of protozoa (EP0232932, WO00006172), binding to PPAR-α and -γ (FR02866339), P2X7 inhibitors (US25288288, WO04058270) and IL-5 production inhibitors (WO09902505).
None of the specifically disclosed compounds are structurally related to the compounds of the present invention. It has now surprisingly been found that the compounds of general Formula I show potent activity and selectivity on GABAB receptor.
The present invention relates to a method of treating or preventing a condition in a mammal, including a human, the treatment or prevention of which is affected or facilitated by the neuromodulatory effect of GABAB modulators.